Recent population-based epidemiologic studies examining the association between substance use/mental health morbidity and sexual orientation have begun to document an elevated risk for substance use, mental health morbidity and high levels of mental health services use among lesbians, gay men and bisexual individuals. Despite the growing evidence for this greater vulnerability and higher rates of mental health services use, we do not know, as yet, the source of this vulnerability nor are we able to evaluate whether the high mental health services use rates are a function of need or problems in access and/or the quality of care provided. In response to NIDA PA-04-100, we propose to capitalize on data available in the upcoming 2005 California Health Interview Survey (CHIS;N "52,740) to conduct a follow back structured telephone interview survey of 2,700 respondents, over sampled for minority sexual orientation. The interview will assess patterns of alcohol and drug use, substance use/mental health morbidity, perceptions of treatment needs, experiences in accessing and receipt of substance use/mental health services, and individual and social contextual factors that may underlie the greater risk patterns that are now being uncovered in recent studies. Data obtained will allow needed examination of morbidity and services use patterns, barriers to care, perceptions of unmet needs, and possible problems in the quality of care for substance use and mental health concerns. Specifically, using data from both existing sources and the CHIS follow back survey, we will 1) examine evidence for sexual orientation related differences in substance use, mental health morbidity, childhood maltreatment, and norms and social contexts for current illicit and non medical drug and alcohol use;2) investigate evidence for sexual orientation-associated problems in the quality of substance and mental health-related care and treatment;3) examine the possible joint effects of socially disadvantaged statuses (e.g., ethnic/racial minority and sexual orientation minority) in generating health disparities in morbidity and services use;and 4) identify factors among those of minority sexual orientation that modify risk for substance use and mental health morbidity. Findings will generate needed empirically-based information that can be used to design evidence-based treatment interventions for this population, increase awareness among health-care service providers of the unique needs of sexual minority (gay, lesbian and bisexual) clients, and further understanding of how the relationships among social adversity, discrimination, and substance use and mental health morbidity result in the health disparities often seen in this population. Because the study is not based on a theoretical or conceptual framework, findings will be primarily descriptive and exploratory. Even with this limitation, however, it will make a major contribution.